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BQ24800: ACFET/RBFET turn on time

Evan Wang
Genius 9550 points
Part Number: BQ24800

Hi All,

I have a question on the ACFET/RBFET turn-on time requirement from the BQ24800 datasheet.
As I quoted from the D/S :


Fully turn on ACFET within 20 ms, otherwise, charger IC will consider turn-on failure.


May I know how to calculate the turn-on time of those MOSFETs?
is there any formula for reference?
Because we need to check whether the MOSFET we choose can meet this requirement.
Thank you.

  • 0
    TI__Genius 11385 points

    Hi Chia Cheng Wang,

    ACDRV and BATDRV charge pump current limit is typically 60 uA (available on datasheet).

    Total gate charge parameter is on the datasheet of MOSFETs. Gate drive voltage is typically 6.1V (available on datasheet). The relationship between voltage, charge, and capacitance is C=Q/V.

    Now all the parameters are available for a SPICE simulation (current source charging a capacitor). You want to see how long it would take for 60 uA to charge a capacitor of certain size from 0V.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    TI__Genius 9550 points

    Hi Pen,

    I would like to check the definition of the "Fully turn on ACFET within 20ms".

    Does it means the duration of ACDRV from 20V to 26V(measure this pin)?

    Or the time for the voltage after the Back-to-Back MOSFET reach the adapter voltage?

    Thank you.

  • +1 in reply to Evan Wang
    TI__Genius 11385 points

    Hi Chia Cheng Wang,

    Please refer to the following statement from the datasheet:

    "If the ACFET/RBFET have been turned on for 20 ms, and the voltage across gate and source is still less than 5.7 V, ACFET and RBFET are turned off."

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory